Pain is significant national health problem, costing the American public more than $100 billion each year. Voltage-gated sodium currents are essential to the generation of action potentials and contribute to the hyperexcitability of nociceptive neurons. However, although sodium channel blockers are useful for preventing acute pain, they are often associated with undesirable cardiac and CNS side effects due to their lack of isoform selectivity, limiting their therapeutic window and their effectiveness in treating chronic and neuropathic pain. Several voltage-gated sodium channels are preferentially expressed in nociceptive neurons (Nav1.7, Nav1.8 and Nav1.8). Nav1.7 in particular has been shown to play an absolutely crucial role in pain, including chronic neuropathic pain. Developing drugs that specifically target these nociceptive sodium channels could substantially increase the therapeutic armamentarium for pain. The majority of sodium channel inhibitors and modulators that have been identified interact with the sodium channel pore - because the amino acid residues lining the pore are highly conserved among the nine sodium channel genes, it has been difficult to identify pore blockers with isoform specificity. By contrast, the voltage-sensors of sodium channels show greater divergence and therefore it should be possible to develop voltage gating modifiers that target specific sodium channel isoforms. We are proposing to harness gating-pore currents to monitor sodium channel voltage-sensor function and enhance our ability to screen for voltage- gating modifiers. These gating-pore currents are currents that selectively flow through the voltage sensor domains of ion channels and provide a direct read-out of the voltage-sensor position. Importantly, they do not reflect pore activity. Two specific aims are proposed: AIM I will determine if gating-pore currents can be used to monitor the activity of voltage-sensor modulators of voltage-gated sodium channels. AIM II will determine if isolated voltage sensors or chimeric bacterial sodium channels containing a single voltage sensor of Nav1.7 can generate gating-pore currents that are sensitive to specific voltage-sensor modulators. Although we initially target Nav1.7 channels because of their importance in pain, this approach should be readily adaptable for identification and characterization of voltage-sensor modulators of other voltage-gated channels and therefore could be used to help identify isoform specific voltage-gated channel modulators that can be used in research and for the development of better therapeutics to treat a multitude of disorders of excitability such as pain, epilepsy and cardiac arrhythmias. PUBLIC HEALTH RELEVANCE: Pain is a serious medical problem that is difficult to treat in many patients. There is exceptionally strong experimental and clinical evidence indicating that drugs targeting a specific protein, Nav1.7, might be especially good at selectively blocking pain sensations. This study develops a new assay for identifying drugs that target the activity of this crucial protein.